Update monitor labels on the stage when language changes

A complete rewrite of OpcodeLabels. Instead of function, it’s a class that maintains a current translator function, and updates the opcode labelFn for each opcode when a new translator function is set. Add function `getLabel` to return the object with `category` and `labelFn` based on the opcode.

Set intl.formatMessage as the translator function in MonitorList. It has access to the intl object, and wraps all monitors.